The invention relates to a solid product based on hydrophobic mineral powder, particularly talcum or mica, having a predetermined characteristic shape that lends itself to handling, especially in the form of a stick. In particular, it concerns a solid product for cosmetic or hygienic use, enabling talcum or mica to be deposited on the skin by contact and gentle rubbing. The invention also relates to a manufacturing method enabling such a product to be obtained with a rigidity and cohesion compatible with its being used without risk of breaking or crumbling.
Talcum is often used in the form of a powder as an active ingredient in cosmetics owing to its emollient properties. The deposit of talcum or the thin film formed protects the skin from redness and irritation, protects the epidermis from rubbing and absorbs excess perspiration. This very old application is carried out by dusting powder on to the surface to be treated and, in practice, is somewhat inconvenient: dusting creates a cloud of powder of greater or lesser size, depending on how fine the talcum is, which pollutes the atmosphere, soils surfaces other than the surface to be treated and leads to material losses.
Furthermore, talcum or mica powder is incorporated in numerous cosmetic formulations as a filler. This mineral powder is generally pressed with active ingredients and fatty binders of the paraffin, lanolin, glycerin or stearate types to obtain a friable paste, which is placed in a pot or tub, generally to be applied using a brush (particularly where make-up products are concerned). In these products, the talcum or mica acts as a filler, which is essentially used to dilute the active ingredient or ingredients into which it is incorporated. This paste contained in the pot or tub has no inherent strength, but, taking into account its packaging, weak cohesion and high friability are acceptable, which enables proportions of talcum or mica of the order of 40 to 50% to be provided, exceptionally reaching 80% in certain products (WO 97/04737 relating to a composition xe2x80x9cwith high levels of talcumxe2x80x9d; xe2x80x9cHandbook of Cosmetic Science and Technologyxe2x80x9d; 1st edition, 1993, p. 134-145, U.S. Pat. No. 4,837,011, EP 0 587 415, WO 98.30195). A high proportion of talcum or mica combined with a relatively low proportion of fatty binder limit the xe2x80x9cgreasyxe2x80x9d effect created by the product when it is applied.
Furthermore, sticks exist for lips (lipsticks or coating sticks) comprising active ingredients and fatty binders, which enable a finishing or protective fatty layer to be deposited on the lips. These sticks have sufficient strength to enable them to be handled but do not generally contain talcum or mica (which are known to have unfavorable effects on particle cohesion). The xe2x80x9cHandbook of Cosmetic Science and Technologyxe2x80x9d cited above provides the most common formulations of this type of sticks (p. 147-155). However, it should be noted that the journal xe2x80x9cCosmetics and Toiletries, April 1992xe2x80x9d gives, on p. 95 and 96, a formulation for a stick for lips containing a small percentage of mica (5%) or talcum (3.65%).
Mineral powders of talcum or mica, and hydrophobic mineral powders more generally, are therefore known to agglomerate with difficulty and to give very friable cakes as soon as the proportion of mineral powder in the product becomes high; this explains why, for more than a century, talcum has been used in the form of a powder when it is intended to be applied alone (or in by far the greatest proportion) as an active cosmetic or hygienic ingredient. For several decades, the development of the numerous formulations referred to above, including talcum or mica as a filler, have only confirmed this teaching, since products with a high load of talcum or mica are products without any inherent cohesion, necessarily contained in pots, tubs or other containers to be applied using an instrument such as a brush, and the very rare stick products containing talcum include very little of it.
It can be noted that certain documents propose the coating of particles of hydrophobic powder to modify their surface properties (U.S. Pat. No. 5,023,075, WO 96.30448); however, it does not appear that the object of this treatment is to make solid products; at any rate, such techniques do not constitute a solution to the problem of the invention, since the characteristics of the initial natural powder are modified.
The present invention proposes the provision of a solid product based on hydrophobic mineral powder, such as talcum or mica, having a rigid shape that enables it to be handled so that a mineral compound can be applied directly by contact with the surface to be treated: the invention aims to avoid in this way the disadvanitages associated with the treatments mentioned above by the dusting of powder.
The object of the invention is in particular to provide a product in the form of a stick or other shape capable of being handled, which is essentially made up of a mineral powder based on talcum or mica (i.e. in which the other components represent less than 20 wt. % of the product) and which benefits from the following features:
inherent cohesion and strength compatible with use by contact without the solid product breaking or crumbling,
good distribution of talcum or mica by contact with the surface to be treated,
dry impression on application, with no greasy effect.
Another object of the invention is to avoid the so-called xe2x80x9cpolishingxe2x80x9d effect, which consists in a reduction in the distribution after several applications.
To this end, the method according to the invention for making such a solid product with a characteristic shape and cohesion making it capable of being handled is characterized in that the hydrophobic mineral powder, particularly mineral powder based on talcum or mica, is impregnated using a volatile liquid binder in proportions by weight such that the proportion of volatile liquid binder is at least equal to 5% and the proportion of mineral powder at least equal to 80%, and in that the resulting impregnated powder is pressed so as to shape it and provide it with cohesion ensuring the rigidity of the product.
xe2x80x9cMineral powder based on talcum or micaxe2x80x9d means a powder in which talcum or mica, or a mixture of the two, represents at least 75 wt. % of the powder (generally more than 85%, preferably more than 95%, or even 100%), any other components being mineral components such as kaolin, carbonate etc., or possibly organic, such as starch etc. xe2x80x9cTalcumxe2x80x9d means either the mineral hydrous magnesium silicate or the mineral chlorite (hydrous magnesium and aluminum silicate), or a mixture of the two. xe2x80x9cMicaxe2x80x9d means aluminous micas such as sericite, muscovite, magnesium micas such as phlogopite, and aluminous or magnesium illites derived from the above minerals by variable substitutions of Al for Si on the one hand, and of Fe for Al or Mg on the other hand.
xe2x80x9cVolatile liquid binderxe2x80x9d means a binder that is liquid at normal temperature and pressure having a volatility, defined by DIN standard 53249, such that the loss of weight is greater than or equal to 30% after 100 minutes at 25xc2x0 C. This type of volatile binder always has a viscosity of less than 50 centipoises.
The term xe2x80x9cpressxe2x80x9d means any operation for compressing grains of powder, particularly the operation of pressing in any press system, extrusion operation etc., the resulting solid product then being removed from the press to be packaged according to its shape and the intended application.
Tests have shown that it was possible to make, using the method of the invention, products based on hydrophobic mineral powder, such as talcum or mica powder, having rigidity and cohesion compatible with good shape stability and handling without breaking or crumbling (during manufacture when removing from the mold and during use), while giving a dry impression when applied to the skin (no xe2x80x9cgreasyxe2x80x9d effect): talcum can thus be used by contact to serve as an active ingredient under the same conditions as traditional talcum powder products capable of being dusted. On contact with the surface to be treated, the product separates on the surface leading to good distribution of the mineral compound and a deposit or film suitable for achieving the desired treatment. No polishing effect is observed, even after a large number of applications (unless the pressing pressures are very high).
The optimum pressing pressures for the impregnated powder depend on the mineral powder and the volatile liquid binder used and on the proportion thereof (and any additives); a pressure of between 200 and 700 kg/cm2 generally gives good results for talcum and mica powders. The impregnated powder is placed in a mold, the shape of which is adapted to the desired shape, and the above pressure is applied in particular using a piston (with evacuation of air).
The shape given to the product during pressing is preferably that of a stick, but may be different, depending on the application: cake, cylinder etc.
The volatile liquid binder used is advantageously a cyclic liquid silicone, particularly from the family of the cyclomethicones with a low degree of polymerization such that its viscosity is less than 10 centipoises, and preferably less than or equal to 5 centipoises. These compounds lead to a product of excellent quality (inherent strength/distribution/dry impression/lack of polishing effect).
It is possible to add to the product a small percentage of organic fatty binder in powder form, particularly the powder of a metal stearate. This addition increases the quality of distribution of the product by contact but also increases the xe2x80x9cgreasyxe2x80x9d effect and the friability. It has been observed that a weight proportion of fatty binder lower than the proportion of volatile liquid binder led to good results; an excellent compromise consists in adding to the hydrophobic mineral powder approximately between 6 wt. % and 9 wt. % of volatile liquid binder and between 2 wt. % and 3 wt. % of metal stearate powder. It should be noted that the products formed with these proportions of fatty binder but in the absence of volatile liquid binder (or with a reduced proportion lower than that of the fatty binder) have very marked friability incompatible with obtaining a stable shape capable of being handled (in the case of a complete absence of volatile liquid binder, a large number of products break when being removed from the mold).
Other additives, such as perfume or emollient, can also be added to the powder in small proportions (i.e. less than or equal to 2%).
The invention also relates to the novel product constituted by a solid shape capable of being handled, particularly a stick, suitable for creating a deposit of mineral compound, such as talcum or mica, by contact, said product comprising a pressed hydrophobic mineral powder impregnated with a volatile liquid binder, the mineral powder representing between 80% and 95% of the total weight and the volatile liquid binder at least 5% of the said weight. The mineral powder is particularly a powder based on talcum or mica because of the cosmetic or hygienic properties of these compounds. In the case of talcum, it is thus possible to make a stick containing, as solids, at least 95% talcum, particularly 100% (weight of talcum in relation to the weight of solids in the product).